Piezoelectric materials convert mechanical stress or strain into signals of electrical energy. The flexibility, robustness and relatively low cost of piezoelectric materials make them particularly suitable for use in sensors.
Piezoelectric sensor systems are used in the collection of traffic data. Such sensors may be temporarily or permanently installed on a road surface across one or more lanes of traffic. Piezoelectric sensors which are configured to collect traffic data may have application as vehicle counters, weight-in-motion sensors, vehicle classification systems, red-light cameras or speed detectors.
In spite of their utility, piezoelectric sensors are prone to certain types of errors. Most sources of error in piezoelectric sensor systems can be broadly classified as vehicle, environment, system or roadway dependent.
In order to achieve optimum performance of piezoelectric sensor systems, sensor installation is a critical factor and care must be taken in selecting a suitable site and installing the apparatus so as to minimise environmental and roadway dependent errors. The piezoelectric sensor system should be located on a straight, flat section of road to minimise speed variations. Similarly, sites approaching or leaving intersections or traffic lights should be avoided. Environment dependent errors may occur due to factors such as vibration, which may generate signals that distort the data collected.
System dependent errors include problems such as scatter and signal reflections. The signal-to-noise ratio for piezoelectric systems is typically relatively poor.
Sources of error dependent on factors such as vehicle dynamics and environmental factors are inherent in all piezoelectric systems and are difficult to compensate for. Therefore, system designers and manufacturers must determine ways in which the impact of system dependent errors such as signal errors can be reduced.
The discussion of the background to the invention included herein is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to were published, known or part of the common general knowledge as at the priority date of the claims.